This invention relates generally to a photoconductor belt assembly employed in an electrophotographic printing machine, and more particularly concerns an improved apparatus for replacing used photoconductive belts in the printing machine.
In an electrophotographic printing machine, a photoconductive belt is charged to a substantially uniform potential so as to sensitize the surface thereon. Thereafter, the charged portion of the photoconductive belt is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive belt selectively discharges the charge thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive belt corresponding to the informational areas contained within the original document being reproduced. After the electrostatic latent image is recorded on the photoconductive belt, the latent image is developed by bringing a developer mix into contact therewith. The developer mix comprises toner particles adhering triboelectrically to carrier granules. These toner particles are attracted from the carrier granules to the latent image forming a toner powder image thereon. The toner powder image is then transferred to a copy sheet. Finally, the copy sheet is heated to permanently affix the toner particles thereto in image configuration. This general approach was originally disclosed by Carlson in U.S. Pat. No. 2,297,691, and has been further amplified and described by many related patents in the art.
Generally, an electrophotographic printing machine utilizes either a photoconductive drum or belt. Various materials have been proposed for photoconductive belts or drums employed in electrophotographic printing machines. One well known material is made from a selenium alloy which is capable of producing a substantially large number of copies before replacement is required. Another material may be of an organic type. However, organic photoconductor materials also have a limited life and require replacement.
A new technique for replacing photoconductive belts utilizes a sub-belt that moves about an endless path in the printing machine. A photoconductive belt is secured releasably to the sub-belt and stripped therefrom when replacement is required. If the path that the sub-belt traverses is constructed as a perfect cylinder, there is little difficulty in accurately mating the photoconductive belt to the sub-belt. However, when the path of the sub-belt takes the shape of a cone, the longitudinal elements of the sub-belt are no longer a straight line but rather arcs of a circle with its center at the apex of the cone. This prevents the placement of a rectangular photoconductive belt sections on the surface of the sub-belt. The path of the photoconductive belt must correspond identically to the conical path of the sub-belt. To achieve the foregoing, the photoconductive belt must be provided with sufficient degrees of freedom to change its angle of approach and position relative to the roller driving the sub-belt. Only under these latter circumstances will the photoconductive belt be secured to the sub-belt in a wrinkle-free state.
Accordingly, it is a primary object of the present invention to improve the apparatus employed in replacing photoconductive belts in an electrophotographic printing machine.